In order to perform an input operation such as adjusting the volume or selecting a song on a small mobile electronic device such as a portable music player, it is necessary to take out the device from a pocket or bag where the device is stored. As a technology for helping the user avoid this action, Patent Document 1 describes a mobile telephone device having parts of its functions attached to an arm.
Further, Patent Document 2 describes a telephone device that is attached to an ear and that performs telephone transmission/reception operation based on a trigger signal generated when the user chews.
Further, Patent Document 3 describes an input apparatus that is configured like a wrist watch and that receives gestures such as “grip,” “release,” “twist,” and “shake” as command input.
Patent Document 1:
    Japanese Patent Kokai Publication No. JP-A-10-051527Patent Document 2:    Japanese Patent Kokai Publication No. JP-A-10-200610Patent Document 3:    Japanese Patent Kokai Publication No. JP-P2002-358149A